In connection with an operation for laminating relatively thin filmy materials such as plastic films or pieces of cloth each having a thickness of about 1 mm or less, an operation of taking out filmy materials one by one from a vessel or the like which contains a large number of filmy materials and then conveying them to a working position is performed in various fields. As conventional such conveying means there has been known a vacuum chucking/conveying system which vacuum-chucks and conveys an article with use of a vacuum chucking device comprising a flat plate-like structure and plural vacuum chucks attached thereto. According to this system, however, there has been a fear that the surface of the article being conveyed may be damaged because the article is filmy and thin. In case of the to-be-conveyed article being a screen-like film having a large number of pores, there has been the problem that air leaks from the pores, making the chucking operation difficult.
On the other hand, as is described in JP (U) 54-41892A, there is known an electrostatic holding device wherein plural electrodes are disposed on an insulator layer, a semiconducting adsorbing layer is laminated thereon, then DC voltage is applied to those electrodes, allowing static electricity to be developed on the adsorbing layer, and an article to be adsorbed is absorbed and held by an electrostatic attracting force. If this electrostatic holding device is applied to conveyance, it is possible to effect adsorbing and conveyance without doing any damage to the article being conveyed. This electrostatic holding device is in wide use in the field in which a fine defect exerts a great influence on product yield, for example in the case of semiconductor wafers, optical glass and films.
In connection with the adsorbing method in the electrostatic adsorbing/conveying system, in JP 2003-282671A and JP2004-120921A there is disclosed a method wherein a pair or plural pairs of electrodes are arranged side by side at fine pitches and voltages opposite in polarity are applied thereto and controlled, allowing only the top of plural laminated to-be-conveyed articles to float or be absorbed efficiently.
In connection a method for peeling a conveyed article in the electrostatic adsorbing/conveying system, in JP 6-71944B there is disclosed a method wherein DC and AC power supplies are used as applied voltage sources and, after turning OFF the power, the electricity remaining on the article is decreased quickly, causing the article to be separated quickly.
In JP 2003-285289A there is disclosed a method wherein electrodes are arranged on an insulating material having flexibility and having concaves and convexes on the bottom surface thereof, thereby intending to improve the positional accuracy of a to-be-conveyed article during chucking or separation.
However, according to the method disclosed in JP 2003-282671A and JP 2004-120921A, it is necessary to provide a controller for controlling the applied voltage to an optimum level at all times. As a result, the device becomes expensive in comparison with an electrostatic adsorbing device of a constant applied voltage type.
According to an embodiment described in JP 6-71944B, several seconds are required for separating a conveyed article from an adsorbing plate and thus in the filed requiring high-speed conveyance there remains a problem in point of conveyance efficiency. In the method disclosed in JP 2003-285289A, since a flexible adsorbing plate is used, the state of contact between the adsorbing plate and the article being conveyed is not constant, resulting in that there occurs a difference in contact pressure of the adsorbing plate for the article at the time of adsorbing or separation. In his case, there is a tendency that rubbing damage, contact damage, or texture offsetting, occurs for a product whose yield is greatly influenced by a fine defect.